Well, meditation trains the mind to be more still, more quiet, and in general to focus not on what-ifs but on the moment as it truly is. Even if there's a lot going on outside of myself, I can take respite internally where there's always some peace keeping a level head.
|What your parents think when you don't answer your phone.|
The asana practice helps too, but it's not quite as obvious how it works. Even if I explain it... if you've never done it - it's all just hearsay. I'll do my best. When I'm in a pose I don't just find a boring middle point and hang out... and I don't power through into the next thing. No, I find a spot where there's a mild discomfort and I sit with it for a bit. It's not serious pain or anything I can't handle. It's comfortable enough that if I focus on my breath then I might not even notice. This is the edge where I sit. Right on the line between "this sucks" and "I love this pose". Now what does this have to do with anxiety and stress? Well if I'm practicing finding this subtle place where it's almost uncomfortable then I learn to see that this spot is not a big deal. I learn my personal boundaries where I can weather the storm and where it's a serious problem.
Later when I'm not on my mat I can start to see when I'm worrying about nothing (because how many of my worries actually happen?) and when it truly is a problem. If I can recognize the non-issues sooner than I waste a lot less time and energy being anxious and I can spend a lot more time enjoying life.